The majority of asylum seekers remain in the UK, with most of them staying illegally, campaigners claim.
Migration Watch UK said only one in four of the 660,000 decisions made on asylum claims between 1997 and 2010 led to the applicant being removed.
The cost of the asylum system, including legal costs, has reached almost £10 billion–or £2 million a day–since 1999.
In a study published ahead of the release of official statistics today, Migration Watch UK found that of the 660,000 cases decided in the 13-year period, 509,000 applicants remain in the UK, 243,000 legally and 266,000 illegally.
Sir Andrew Green, chairman of the campaign group, said: “The asylum system has proved to be a £10bn shambles.
“Those who, like ourselves, are serious about protecting genuine refugees should be no less serious about removing bogus claimants and, better still, deterring them in the first place.”
The analysis showed that some form of protection was granted in 243,000 cases, leaving 417,000 which were refused and should have left the UK.
But 36 per cent (151,540) of those denied asylum were removed and a further 8,615 were later established to have left the country without notifying the authorities.
Some 266,000 have neither left nor been removed and are therefore presumed to remain in the UK illegally, Migration Watch UK said, adding that it was possible that some of these may have been granted indefinite leave to remain if they were included in the backlog of more than 400,000 so-called legacy cases.
Of these, 38,000 were removed and 161,000 granted settlement, with 40,500 being put into a “controlled archive”, meaning the UK Border Agency cannot trace them.